Spherical Anatase Research Articles

Optimizing the green synthesis of antibacterial TiO2 - anatase phase nanoparticles derived from spinach leaf extract

Titanium dioxide nanoparticles, renowned for their abundance, non-toxicity, and stability, have emerged as indispensable components in various fields such as air purification, healthcare, and industrial processes. Their applications as photocatalysts and antibacterial agents are particularly prominent. The synthesis methods significantly influence the properties and subsequent applications of these nanoparticles. While several techniques exist, the biological approach using plant extracts offers advantages such as simplicity, biocompatibility, and cost-effectiveness. This study focused on the green synthesis of titanium dioxide nanoparticles utilizing spinach leaf extract. Within the scope of this investigation, the green synthesis of titanium dioxide nanoparticles through spinach leaf extract were synthesized and optimized, followed by a comprehensive examination of their morphological, structural, and chemical attributes with UV-visible spectroscopy, FTIR spectroscopy, XRD, FESEM, and EDX. The minimum inhibitory concentration (MIC) against E. coli and S. aureus was determined to evaluate their antibacterial potential. Optimal synthesis conditions were identified at 50 °C, using a 1/30 concentration and 20 ml of spinach leaf extract. Spherical anatase nanoparticles, ranging from 10 to 40 nm, were produced under these conditions. The change in the color of the extract, absorption at 247 nm, change and increase of the peak at 800 − 400 wavelengths, and the maximum intensity of X-ray diffraction at the angle of 25.367 with the crystal plane 101 were indications of the synthesis of these nanoparticles. Notably, the synthesized nanoparticles exhibited antibacterial activity with MIC values of 0.5 mg/ml against E. coli and 2 mg/ml against S. aureus. This research presents a novel, eco-friendly approach to synthesizing titanium dioxide nanoparticles with promising antibacterial properties.

In situ boro-mullite phase formation in Glass–Ceramic glazes: Anatase–rutile phase transformations and microstructure properties

‘‘Boro-mullite’’ is the name for mullites produced through the synthesis of boron-rich material and playing a critical role in producing high-performance materials. Also, the stability of the anatase phase in the glaze and against temperature has been addressed and improved by many studies. In situ boro-mullite crystals generated using various glass-ceramic glaze compositions that contain TiO2 and their impact on the transformation of anatase into a rutile phase were examined in this study. Additionally, the samples' water absorption, bulk density, apparent porosity and shrinkage, Vickers hardness, and optical properties were evaluated at various Al2O3 and B2O3 amounts at 700 °C, 800 °C, 900 °C, 1000 °C and 1100 °C. X-ray diffraction analysis revealed that as the temperature and Al2O3 ratio rose, it triggered the boro-mullite phase formation. On the other hand, increasing the Al2O3 ratio led to a rise in the samples' sintering temperature and delayed the anatase to rutile phase transformation. Furthermore, the presence of corundum crystals retarded the anatase crystal size growth during the remodelling process of the conversion of anatase to rutile. While the increase in the B2O3 ratio sharpened the peaks of albite crystals, the formation of rutile crystals accelerated with the increase in temperature and caused inhibition of albite formation. The albite phase's presence facilitated the creation of the liquid phase and achieved the 0.010 % water absorption and 0 % apparent porosity values as well the highest bulk density and microhardness with 2.476 g/cm3 and 550 H V. The yellowness (+b∗) values were found to be the highest at 1100 °C where the rutile crystals reached their maximum size. The anatase-rutile conversion is postponed and the increase in the yellowness value is prevented by the glaze's formation of boro-mullite. FESEM-EDS analysis showed that the temperature was the driving force in the transformation of acicular boro-mullite crystal into highly acicular prismatic needle crystal and spherical anatase crystals into the rod shape rutile.

Impact of polymorphism vs. shape of titania nanocrystals on the hydrogen evolution reaction.

Herein, we investigated the impact of polymorphism vs. dimension control of titania nanocrystals towards hydrogen generation. Two different forms of titania nanoparticles have been synthesized following the solvothermal method, leading to the formation of two distinct physicochemical features. Detailed structural, morphological, and optical studies revealed that the formation of titania nanorods correspond to rutile while granular particles correspond to the anatase phase. Among various titania polymorphs, anatase is well known for its superior photocatalytic activity; however, to our surprise, the as-synthesized rutile nanorods exhibited higher catalytic activity in comparison to anatase spheres, and hydrogen evolution was considerably enhanced after the addition of a minute amount of Pt as the co-catalyst. Thus, despite the higher catalytic activity of anatase, the enhanced hydrogen evolution of rutile nanorods may be related to the creation of a 1D structure. Our study highlights the importance of considering not only TiO2 polymorphism but also shape and dimension in optimizing photocatalytic H2 production.

Synthesis and characterizations of molybdenum-doped titanium dioxide nanoparticles for photocatalytic removal of chromium (VI) from aqueous solutions

The photocatalytic removal of toxic heavy metals using titanium dioxide nanoparticles is an emerging technology for environmental remediation. Pure and Mo-doped TiO2 nanoparticles were synthesized using a modified sol-gel process, and then characterized by field emission scanning electron microscopy (FE-SEM) and particle size analysis (PSA) to determine their morphology and size, while X-ray diffraction (XRD) and energy-dispersive X-ray spectroscopy (EDS) were used to determine their crystalline phase and composition. Brunauer–Emmett–Teller (BET) analysis was used to measure the surface area and porosity of the synthesized catalysts applying Langmuir and BET models. The catalyst was mainly composed of spherical anatase TiO2 particles, with a diameter in the range of 15–75 nm, and the maximum doping percentage of Mo was 3.3%. The Langmuir surface area of pure and Mo-doped TiO2was 91.63 and 128.73 m2/g, and the average pore volume was 0.029 and 0.032 cm3/g, respectively. The nanomaterials were used in the photocatalytic removal of Cr(VI) from aqueous solutions, and the adsorption isotherms indicated that the catalyst uptake (qe,max) amounts for Mo-doped TiO2 and pure TiO2 were 12.5 and 6.5 mg/L, respectively. Moreover, the equilibrium removal percentage was improved from 41% for pure TiO2 to 90% for Mo-doped TiO2, which confirms that photocatalytic activity is enhanced by doping TiO2 with molybdenum.

Micro spherical anatase phase TiO2 thin films for room temperature operated formaldehyde gas sensor applications

A highly sensitive and selective gas sensor is crucial for detecting hazardous gases in the environment at room temperature (RT). Titanium dioxide (TiO2) shows promise as an excellent candidate for gas sensing due to its superior sensitivity and stability, even in robust conditions. TiO2 could potentially replace volatile organic compound (VOC) gas sensors. This study employed the spray pyrolysis technique to deposit titania thin films. The precursor solution was sprayed onto substrates at temperatures ranging from 375 °C to 450 °C in 25 °C increments. A temperature-dependent study was conducted on TiO2 thin films to examine their structural, optical, and topographical properties. Films deposited at 400 °C and above exhibit a crystalline anatase phase. Higher deposition temperatures resulted in the decreased band gap of TiO2 films. TiO2 films showed excellent response to formaldehyde concentrations (1–25 ppm) and high selectivity over other reducing gases (methanol, ethanol, butanol, toluene, xylene), even at room temperature. Microstructural, optical, and morphological analyses provided valuable insights into the gas sensing mechanism, enhancing understanding of film functionality.

Annealing temperature influences the cytocompatibility, bactericidal and bioactive properties of green synthesised TiO2 nanocomposites

Annealing is a crucial functional parameter relevant to the green synthesis and bactericidal properties of TiO2 nanocomposites (TiO2-NPs). In this work, the effect of the annealing temperature on the physicochemical, bactericidal and cytocompatibility properties of TiO2-NPs obtained from Calotropis gigantea was comprehensively studied. Results indicated that amorphous-phase TiO2-NPs were transformed into the anatase phase at 500 °C with a crystallite size of 40.9 nm and MIC of 100 mg/mL towards Staphylococcus aureus. Whereas TiO2-NPs annealed at 400 °C demonstrated no bacterial reduction, TiO2-NPs annealed at 500 °C showed a moderate zone of inhibition towards Escherichia coli and Pseudomonas aeruginosa. Findings from this study found that TiO2-500C nanocomposites concentration at 100 mg/mL does not inhibit fibroblast cells proliferation activity after 24 h treatment. The plant-mediated nano-sized cubic and spherical anatase TiO2-NPs encapsulated bioactive green elements, such as carbon, sodium, magnesium, chlorine, potassium, calcium and sulphur, from the C. gigantea extract, ultimately leading to versatile and eco-friendly bactericidal agents with wound-healing properties. Further studies involving in vivo are needed to support this work.

Hydrothermal Separation of Titanium Vanadium and Chromium from a Pregnant Oxalic Acid Leachate.

The separation of titanium, vanadium and chromium in vanadium slag (VS) is a difficult problem restricting the comprehensive utilization of VS. This paper presents the first study on the separation of titanium, vanadium and chromium from oxalic acid leachate of VS. Firstly, the separation of titanium from the leachate by hydrothermal method was studied. The results show that more than 99% of titanium in the leachate was precipitated in the form of spherical anatase TiO2 with the purity of 95.7%. Then, the extraction separation of vanadium and chromium from the titanium-free filtrate by three-stage extraction of acidified N235 extractant and four-stage stripping of HCl solution was investigated. The extraction mechanism was identified as the anion exchange reaction between acidified N235 extractant and vanadium and chromium complex anions, which were further stripped by HCl solution in the stripping process. After obtaining the concentrated and purified stripping solution containing vanadium and chromium, the separation of vanadium and chromium from the stripping solution by hydrothermal method was studied, and the product was mainly composed of VO2 and Cr2O3. This process provides an idea for the comprehensive utilization of titanium, vanadium and chromium in oxalic acid system.

Rational synthesis of SrTiO3 nanodots anchored mesocrystalline anatase TiO2 submicrospheres for photocatalytic reduction of CrVI

A novel spherical anatase TiO 2 mesocrystal/SrTiO 3 heterojunction with favored Cr VI adsorption, bolstered charge carrier separation and well-preserved reduction capability was successfully produced, which exhibited enhanced activity toward photocatalytic reduction of Cr VI . • Spherical anatase mesocrystal/SrTiO 3 nanodot type-II heterojunction was prepared. • Favored Cr VI adsorption and bolstered charge carrier separation were realized. • The heterojunction showed remarkably enhanced photocatalytic reduction of Cr VI . Mesoporous anatase TiO 2 sphere based materials has long been the focus of intensive research dealing with environmental-related issues due to their significant advantages in terms of structural isotropy, high surface area, structural stability, and low cost. However, in most cases, the employed mesoporous anatase spheres were comprised of nanocrystalline subunits with random crystalline orientations, which means that numerous grain boundaries exist in the sphere-shaped particles, suppressing their performance in various applications. Herein, by using mesocrystalline anatase submicrospheres that were synthesized via utilizing SO 4 2- ions to modulate the growth dynamics of anatase crystals in the green mixed solvents of PEG-400 and H 2 O as both template and reactant, novel sphere-shaped anatase mesocrystal/SrTiO 3 nanodot heterostructures were successfully produced. These spherical anatase mesocrystal/SrTiO 3 heterostructures exhibited noticeably enhanced activity toward reduction of hexavalent chromium (Cr VI ) under stimulated solar light irradiation, which was largely attributed to their favored adsorption of Cr VI , bolstered photogenerated charge carrier separation and well-preserved reduction capability due to the construction of a well-defined type-II heterojunction with tight interfacial contacts and strong interactions. This work will be useful for the designed fabrication of micro/nanostructured TiO 2 based photocatalysts with complex spherical morphologies for photocatalytic applications in environmental purification.

Absorption mechanism of dopamine/DOPAC-modified TiO2 nanoparticles by time-dependent density functional theory calculations

Donor-modified TiO2 nanoparticles are interesting hybrid systems shifting the absorption edge of this semiconductor from the ultra-violet to the visible or infrared light spectrum, which is a benefit for several applications ranging from photochemistry, photocatalysis, photovoltaics, or photodynamic therapy. Here, we investigate the absorption properties of two catechol-like molecules, that is, dopamine and DOPAC ligands, when anchored to a spherical anatase TiO2 nanoparticle of realistic size (2.2 nm), by means of time-dependent density functional theory calculations. By the differential absorbance spectra with the bare nanoparticle, we show how it is possible to determine the injection mechanism. Since new low-energy absorption peaks are observed, we infer a direct charge transfer injection, which, unexpectedly, does not involve the lowest energy conduction band states. We also find that the more perpendicular the molecular benzene ring is to the surface, the more intense is the absorption, which suggests aiming at high molecular packing in the synthesis. Through a comparative investigation with a flat TiO2 surface model, we unravel both the curvature and coverage effects.

Dendritic mesoporous silica&titania nanospheres (DMSTNs) coupled with amorphous carbon nitride (ACN) for improved visible-light-driven hydrogen production

Dendritic mesoporous silica nanospheres (DMSNs) are very promising platforms for catalysis application and other catalytic materials can be decorated into their nanochannels. Herein, we present a strategy of introducing two types of catalytic components to DMSNs nanochannels for the first time. Initially, dendritic mesoporous silica&titania nanospheres (DMSTNs) were fabricated with spherical anatase titanium oxide (TiO2) nanoparticles uniformly dispersed in dendritic channels. Then, multilayer amorphous carbon nitride (ACN) nanofilm was coated onto DMSTNs interfaces. The as-prepared heterogeneous DMSTNs/ACN photocatalysts maintain excellent dendritic architecture and display significantly improved visible-light response. DMSTNs/ACN can produce 9600 μmol·g−1 H2 with a ca. 1900 μmol·g−1·h−1 rate in 5 h for water splitting under simulated sunlight condition, greater than those of DMSTNs and DMSNs. The novel catalyst can also generate 7.09 μmol·g−1 CO (49.10%) and 6.86 μmol·g−1 CH4 (50.90%) in carbon dioxide reduction with its specific selectivity. This investigation opens up the possibility of adopting ACN-coated DMSTNs as novel photocatalysts for energy conversion in visible light environment.

Phase-dependent performance of lotus-root shaped TiO2 anode for lithium-ion batteries (LIBs)

We had reported the lotus-root shaped meso-/macroporous TiO2 (LR-TiO2) for the photoanode of DSSCs and also the synergistic interfacial electron transfer of coexisting anatase and rutile phases in a mesoporous TiO2 particle. Thus, we were to investigate phase-dependent performance of LR-TiO2 as an anode for LIB comparable to DSSCs mechanistically, whose crystalline phase was controlled by simply varying the calcination temperature. SEM measurements showed the unchanged morphological characteristics of columnar macroporous channels favorable for Li+ supply regardless of the calcination temperature. However, anatase- and rutile-rich phases were confirmed by PXRD measurements for LR-TiO2 calcined at 450 °C (LR-TiO2-450) and 700 °C (LR-TiO2-700), respectively. The capacity of the LR-TiO2-450 anode was 120 mAh g-1 and the capacity of LR-TiO2 decreased with the increase of calcination temperature. It is basically attributed to a better electrical conductivity of anatase to rutile and loss of surface area due to a poor stacking of larger rod-like rutile granules compared to smaller spherical anatase ones. However, we could not specify the expected synergistic effect of mixed phase in LR-TiO2-550 because the resistance of electron transfer is not significant compared to that of Li+ transfer based on EIS measurements. Correspondingly, high rate performance showed the higher capacity decrease as the C-rate increased.

Synthesis and luminescence of Eu3+ doped nanocrystalline TiO2 spheres

Eu3+ doped TiO2 anatase spheres were obtained by modified sol-gel approach. Spheres (110–250 nm) are composed of smaller (5–15 nm) nanocrystals and exhibit red emission under UV light excitation. Materials were synthesized by multi-step method from glycolated titania alkoxides. Europium doped (1.0 mol%) and non-doped spheres were synthesized. Their optical and structural properties were compared by materials characterization methods, such as X-ray powder diffraction, transmission electron microscopy and PL spectroscopy. Doped TiO2 spheres are crystalline phase pure and exhibit high luminescence intensity.

TiO2 hollow spheres with separated Au and RuO2 co-catalysts for efficient photocatalytic water splitting

Abstract Hollow mesoporous TiO2 photocatalysts with dual co-catalysts, located at specific positions, were prepared using Polystyrene (PS) as sacrificial templates. Au nanoparticles (NPs) were in situ loaded on the surface of PS spheres and the resulting nanocomposites were coated with TiO2 shell using sol-gel reaction. The outer surface of core-shell spheres was impregnated with Ru and the subsequent calcination produced hollow anatase spheres with Au and RuO2 dual co-catalysts. The hollow mesoporous spheres of Au@TiO2@RuO2 were proved by various techniques such as TEM, EDX, and SEM images. Photocatalysts were applied for hydrogen generation from water splitting and that with dual co-catalysts showed efficient catalytic activity under simulated solar light. The catalytic activity of photocatalysts with both oxidation and reduction co-catalysts (Au@TiO2@RuO2) showed hydrogen evolution (3165 μmol g−1) almost two times more than that Au@TiO2 and TiO2@RuO2 with single co-catalysts. And the hydrogen evolved is more than three times as compared to TiO2 (935 μmol g−1) without any co-catalyst. Hollow mesoporous morphology with different co-catalysts on inner and outer surfaces is believed to enhance photocatalytic activity which is due to better separation of photo-generated charges.

Ti3+-doped TiO2(B)/anatase spheres prepared using thioglycolic acid towards super photocatalysis performance

A high efficiency photocatalyst, TiO2(B)/anatase spheres consisted of nanosheets were prepared. Thioglycolic acid (TGA) was added into the precursor to control the hydrolysis process of titanium source (TiCl3), which is a key to adjust the microstructure of products. The results indicated that TGA-modified samples revealed enhanced photocatalysis performance compared with the one without TGA. The photocatalysis performance of TGA-modified sample is about 15 times high compared with commercial P25. This is ascribed to mixed crystal phase and lattice distortion which resulted in more activity sites (e.g. Ti3+ and oxygen defects). The loading of Au nanoparticles in different ways confirms that rich Ti3+-oxygen vacancies on the surface of samples caused super photocatalytic performance.

A photoelectrochemical aptasensor constructed with core-shell CuS-TiO2 heterostructure for detection of microcystin-LR

In this work, a CuS-TiO2 heterojunction composite was prepared by dispersedly depositing CuS nanoparticles on TiO2 nanospheres surface with a hydrothermal method, and was then used to construct a photoelectrochemical (PEC) aptasensor for sensitive detection of microcystin-LR (MC-LR) in aquatic environment. The energy bands of CuS nanoparticles and spherical anatase TiO2 were well matched, which enhanced the photo-to-current conversion efficiency. The composite exhibited the enhanced visible light absorption, the improved separation of photo-generated charges, and the reduced self-aggregation of CuS nanoparticles, leading to the enhanced photocurrent response. The PEC aptasensor was constructed by immobilizing CuS-TiO2 composite on ITO electrode with chitosan film that further covalently bound aminated aptamer. After the target, microcystin-LR (MC-LR) as an analyte model, was captured by the aptamer on the aptasensor, it could be oxidized by the photo-generated hole to impede the electron-hole recombination and further amplify the photocurrent. The PEC aptasensor showed superior analytical performance for MC-LR with a linear range of 5.0 × 10−5 nM to 250 nM and a detection limit of 2.0 × 10−5 nM. The detection results with the aptasensor for practical water samples indicated its promising application in environmental monitoring.

Synthesis of Hollow Mesoporous TiO2 Microspheres with Single and Double Au Nanoparticle Layers for Enhanced Visible-Light Photocatalysis.

A facile method was used to prepare hollow mesoporous TiO2 and Au@TiO2 spheres using polystyrene (PS) templates. Au nanoparticles (NPs) were simultaneously synthesized and attached on the surface of PS spheres by reducing AuCl4- ions using sodium citrate which resulted in the uniform deposition of Au NPs. The outer coating of titania via sol-gel produced PS@Au@TiO2 core-shell spheres. Removing the templates from these core-shell spheres through calcination produced hollow mesoporous and crystalline Au@TiO2 spheres with Au NPs inside the TiO2 shell in a single step. Anatase spheres with double Au NPs layers, one inside and another outside of TiO2 shell, were also prepared. Different characterization techniques indicated the hollow mesoporous and crystalline morphology of the prepared spheres with Au NPs. Hollow anatase spheres with Au NPs indicated enhanced harvesting of visible light and therefore demonstrated efficient catalytic activity toward the degradation of organic dyes under the irradiation of visible light as compared to bare TiO2 spheres.

Investigation on Zr-, Hf-, and Ta-doped submicrometric beads for DSSC photoanodes

This paper investigates the effect of Zr, Hf, and Ta doping on the performances of Dye-sensitized solar cells (DSSCs) with photoanodes comprising mesoporous hierarchical anatase spheres. Morphology, structure, and optical properties of doped and undoped materials were examined by Field Emission Scanning Electron Microscopy, X-ray diffraction, and Diffuse Reflectance Spectroscopy, and materials’ characteristics were related to DSSC fundamental photovoltaic parameters by polarization curves (under illumination and dark conditions) and external quantum efficiency measurements. Photoanodes’ charge transport and recombination properties were investigated by Electrochemical Impedance Spectroscopy. Although doping were carried out by inserting a small amount (from 0.1 to 0.3 at %) of homo and aliovalent and electron-rich (with respect to Ti4+) cation, energy conversion efficiency turned out to be lower than pure anatase photoanodes. Electron-impurity scattering phenomena in conjunction with reduced specific surface area caused by the increased bulk free energy are believed to account for the efficiency drop. However, a small beneficial effect introduced by doping on the trap-mediated recombination mechanisms has been identified.

Controlled Assembly of Nanorod TiO2 Crystals via a Sintering Process: Photoanode Properties in Dye-Sensitized Solar Cells

We present for the first time a synthetic method of obtaining 1D TiO2 nanorods with sintering methods using bundle-shaped 3D rutile TiO2 particles (3D BR-TiO2) with the dimensions of around 100 nm. The purpose of this research is (i) to control crystallization of the mixture of two kinds of TiO2 semiconductor nanocrystals, that is, 3D BR-TiO2 and spherical anatase TiO2 (SA-TiO2) on FTO substrate via sintering process and (ii) to establish a new method to create photoanodes in dye-sensitized solar cells (DSSCs). In addition, we focus on the preparation of low-cost and environmentally friendly titania electrode by adopting the “water-based” nanofluids. Our results provide useful guidance on how to improve the photovoltaic performance by reshaping the numerous 3D TiO2 particles to 1D TiO2-based electrodes with sintering technique.

Monodispersibility and size control in the preparation of spherical titania particles by thermal hydrolysis of TiCl4 in various solvents

Spherical anatase TiO2 particles were successfully synthesized by the thermal hydrolysis of TiCl4 in various solvents. In the case of n-propanol, isopropanol, and acetone with an RH ratio of 3, spherical titania particles were produced. In contrast, spherical TiO2 particles did not form in methanol and ethanol because of their high dielectric constants. In this study, different oscillators (an oven, and isothermal and ultrasonic oscillators) were used to prepare titania prior to studying the morphology and particle size. The spherical TiO2 particles prepared using the ultrasonic oscillator were much smaller than those obtained using the other heating methods, because of the lower temperature gradient in the solution; however, a narrower size distribution of particles was observed in the TiO2 prepared in an oven. The presence of acetylacetone as a dispersing agent in the starting solutions significantly reduced the particle size. The optimum concentration of acetylacetone of 0.8mg/cm3 resulted in more uniform TiO2 spheres with an average particle size of 1.4µm.

In situ FT-IR study on the homogeneous nucleation of nanoparticles of titanium oxides from highly supersaturated vapor

The formation of nanoparticles of titanium oxides by homogeneous nucleation from highly supersaturated vapors was investigated by in situ Fourier transform IR spectroscopy and by observation of the resulting nanoparticles by transmission electron microscopy (TEM). Titanium metal was thermally evaporated in a specially designed chamber under a gaseous atmosphere of oxygen and argon. Nanoparticles nucleated and subsequently grew as they flew freely through the oxidizing gas atmosphere. Nascent nanoparticles of titanium oxides showed a broad IR absorption band at 10–20 μm. Subsequently, the cooled nanoparticles showed a sharp crystalline anatase feature at 12.8μm. TEM observations showed the formation of spherical anatase nanoparticles. The IR spectral evolution showed that the titanium oxides nucleated as metastable liquid droplets, and that crystallization proceeded through secondary nucleation from the supercooled liquid droplets. This suggests that history of the titanium oxide nanoparticles, such as the temperature and oxidation that they experience after nucleation, determines their polymorphic form.